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2001 Ranger 4.0 surging when HVAC is turned on


Viva*the*Ranger

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Hey folks! It's been a long time, but I'm back with a problem..

My wife's 01' 4.0 runs and idles fantastic, except when the HVAC is turned to anything (but) floor only or vent only. With those on it's just fine. When I turn it to AC, floor/vent and defrost, it will idle really low like 500RPMS and the AC compressor will kick on, and it almost dies, then back to 500 ad so-on. It will do this every few seconds. I saw another thread about something similar here on the forums, but I think this might be different.

I checked very thoroughly for vacuum leaks and pulled the IAC off and cleaned it out. It didn't seem too dirty, and all the vac lines are in good shape and connected properly. The truck is not throwing any codes. Any ideas what's going on here?

Thanks in advance :beer:

Chris
 


RonD

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In 2001 the PCM(computer) is part of the AC system, it has been since PCMs and fuel injection were used, just more so in '01.
When you select AC or Defrost the compressor needs to start, this will of course drop engine RPMs unless PCM opens IAC valve a bit more
(PCM should do the same thing when you put an automatic trans in gear, bump up RPM by opening IAC Valve.)

When you select AC, for example, the switch sends 12volts to the PCM(pin 41)
The PCM then Grounds the AC Clutch Relay in the engine fuse box, which sends 12volts to the AC Clutch and compressor engages, dropping RPMs if PCM hasn't opened IAC Valve a bit.
So PCM is actually controlling AC clutch directly, in older system the PCM just got the 12volts when Clutch did, simple splice, so it knew when to bump up the idle.

The Ground the PCM use for the Clutch Relay is from the two Pressure switches on the AC lines, low pressure and high pressure switches, if either is open then compressor will either not work or cycle on and off as switch opens and closes.

There is no Vacuum associated with the AC system, and a vacuum leak usually causes higher RPMs.

So......PCM is getting the 12volts from the cab switch or clutch wouldn't work at all.
But PCM is not bumping up the idle
Or compressor is drawing too much power, failing bearing, long shot
 

Denisefwd93

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Possible refrigerant over charge, compressor tight ready to lock up. too much oil in compressor.
 

Viva*the*Ranger

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In 2001 the PCM(computer) is part of the AC system, it has been since PCMs and fuel injection were used, just more so in '01.
When you select AC or Defrost the compressor needs to start, this will of course drop engine RPMs unless PCM opens IAC valve a bit more
(PCM should do the same thing when you put an automatic trans in gear, bump up RPM by opening IAC Valve.)

When you select AC, for example, the switch sends 12volts to the PCM(pin 41)
The PCM then Grounds the AC Clutch Relay in the engine fuse box, which sends 12volts to the AC Clutch and compressor engages, dropping RPMs if PCM hasn't opened IAC Valve a bit.
So PCM is actually controlling AC clutch directly, in older system the PCM just got the 12volts when Clutch did, simple splice, so it knew when to bump up the idle.

The Ground the PCM use for the Clutch Relay is from the two Pressure switches on the AC lines, low pressure and high pressure switches, if either is open then compressor will either not work or cycle on and off as switch opens and closes.

There is no Vacuum associated with the AC system, and a vacuum leak usually causes higher RPMs.

So......PCM is getting the 12volts from the cab switch or clutch wouldn't work at all.
But PCM is not bumping up the idle
Or compressor is drawing too much power, failing bearing, long shot
First of all, thank you very much for the info! So if I'm reading this right (which I'm probably off a bit) It sounds like the PCM might be sending a bad signal to the IAC, or non at all when asked to use the ac clutch? I recently did valve cover gaskets on it. Do you think when I unhooked the main harness, maybe pin 41 got some gunk on it, or isn't seated right? So maybe try pulling it back off, and spraying lectra-clean on both sides/unhook the battery for 30 mins and put it back together?

Possible refrigerant over charge, compressor tight ready to lock up. too much oil in compressor.
We didn't do any recharging on the AC. I'm very mechanical, but don't know anything about AC's.. what do you mean by too much oil in the AC? Thanks!

Chris
 

RonD

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PCM is getting the signal/12volts on pin 41, or compressor wouldn't start, so that is working.

When you cold start an engine the computer should run idle RPMs higher, about 1,100, and then as engine warms up RPMs will slowly drop down to "target" RPM, automatic 750, manual 650
If that is happening then computer has good control of IAC Valve
 

Viva*the*Ranger

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That's exactly right. It will idle fantastic until I turn the hvac. If this was your truck, where would you look first for failure? Thanks
 

Viva*the*Ranger

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Well, I think it's fixed! I decided to unhook the battery while changing the oil. Once all back together, the problem went away. Maybe the PCM just didn't get things right after being unhooked for a couple days while replacing the valve cover gaskets, water pump and a few other things.

Fingers crossed! Thanks for the information guys. I really appreciate it!

Chris
 

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